Apparatus for printing by reverse lithography

ABSTRACT

A reverse lithographic printing apparatus incorporating a combined inking and fountain roller is disclosed. A watermiscible ink is applied to the surface of an oil loaded, porous inking roller. A mixture of ink and oil is formed which is applied to the printing master. The oil selectively deposits on the oleophilic background portion of the master while the watermiscible ink selectively deposits on the image areas.

United States Patent [191 Kaminstein 3,797,388 1 Mar. 19, 1974 APPARATUS FOR PRINTING BY REVERSE LITHOGRAPHY [75] Inventor:

[73] Assignee: Ing. C. Olivetti & C0., p.A., Ivrea,

Italy 22 Filed: Dec. 7, 1971 21 Appl. No.: 205,522

Bernard Kaminstein, Paramus, NJ.

[52] US. Cl. ..101/141,101/148,101/367, 101/451 [51] Int. CI B4lf 7/36 [58] Field of Search ..101/147,148, 367

[56] References Cited UNITED STATES PATENTS 1.201.599 10/1916 Lutz ..101/451 3.690.252 9/1972 Sokolov 101/147 3.513.000 5/1970 Vrancken et al. 101/450 X 2.965.911 12/1960 Hempel et a1. 101/367 X 37.727 2/1863 Reynolds 101/367 X 168.511 MacDonald et a1. 101/367 X 2.588.470 3/1952 Bassist 101/142 3,002,449 10/1961 Sherman 441.660 12/1890 Harrison et all. 101/367 X FOREIGN PATENTS OR APPLICATIONS 903,724 8/1962 Great Britain 101/450 957.533 5/1964 Great Britain 101/148 Primary Examiner-Clyde I. Coughenour Attorney, Agent, or FirmLindenberg, Freilich &

Wasserman [57] ABSTRACT A reverse lithographic printing apparatus incorporating a combined inking and fountain roller is disclosed. A water-miscible ink is applied to the surface of an oil loaded, porous inking roller A mixture of ink and oil is formed which is applied to the printing master. The oil selectively deposits on the oleophilic background portion of the master while the water-miscible ink selectively deposits on the image areas.

13 Claims, 10 Drawing Figures PATENTEDK'ARIQ 19w 3.797.388

SHEET 1 BF 4 F I6. I

PATENTEBIARIQ 1914 I 3.797.388

same or 4 ROTATION OF 20 FIG. 4

INVENTORI BERNARD KAMINSTEI N PATENIEDIIARIB m4 3.797.388

SHEU a or 4 INVENTOR. BERNARD KAMlNS TEIN PAIENTEUIARIQ 1914 37971388 SHEET h 0F 4 20s ZIO/ZO4 INVENTOR.

BERNARD KAMINSTUN APPARATUS FOR PRINTING BY REVERSE LITHOGRAPHY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates-to an inking system for a lithographic-type of printing master and, more particularly, to improvements in application of ink and fountain solutions to a printing master for reverse lithography.

2. Description of the Prior Art:

Lithographic printing is based on the mutual immiscibility of aqueous liquids and non-polar organic liquids. In conventional lithographic printing, a printing plate is employed in which an aqueous fountain solution is attracted and retained by the non-image areas and the oil or greasy ink covers the image areas from which it is subsequently transferred either directly to the stock being printed or as in off-set printing to a rubber blanket from which it is then transferred to the stock to be printed. The oil-based inks have objectionable odors which render conventional lithographic printing unsuitable for many purposes, particularly in the food packing industry.

In reverse lithography, the printing plate or duplicating master has non-image areas which preferentially attract a water-soluble or miscible ink repelling liquid. A water-miscible ink is defined according to the invention as an ink formulated with water or a liquid miscible with water such as a glycol. The water-iniscible ink is preferentially retained by the image areas and issubsequently transferred to the stock to be printed. In copending application, Ser. No. 711,519, filed Mar. 8, 1968, now abandoned, entitled Method of Printing and Ser. No. 807,325, filed Mar. 14, 1969, now patent number 3,608,483, entitled Inking System for Printing," printing processes employing reverse lithographic printing plates are disclosed.

These printing processes employ a printing plate or master formed on a smooth, support sheet suitably a clear, thermoplastic resin, such as polystyrene or polyethylene which is selectively wettable by oily liquids. The image pattern is supported on the sheet and is composed of a roughened, coarse, and porous pattern of material selectively attractive to aqueous, miscible printing inks. The non-image areas of the sheet are rendered repellent to the inks by applying a film of an aqueous immiscible liquid such as a nonpolar, hydro,- phobic hydrocarbon liquid to the sheet. It has been found in practice that the liquid must be frequently reapplied to the printing plate usually after several copies have been reproduced or the nonprinting areas take up some ink with result that the background areas of the prints become dirty.

The oily background liquid has been applied to the printing plate from a separate applicator employing a reservoir of oily fountain solution and rollers to apply the oil directly to the plate or to a train of rollers proceeding the inking rollers so that the oil is milled into the ink before the ink reaches the final inking or form rollers which ink the printing master.

In the printing processes employed to date, the metering and control of the background fountain solution must be fairly strictly controlled in order to assure that high quality prints are produced. This has required the complex mechanisms for applying the liquid such as oil drop control mechanisms and separate reservoirs and application rollers.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is to provide a simpler arrangement than heretofore employed for applying oily fountain solution to planographic printing plates for reverse lithography.

A further object of this invention is to provide an improved reverse lithographic process in which the printing master is simultaneously inked and wetted with fountain solution and thereafter produces excellent prints.

Still another object of this invention is to improve the retention of ink in the image areas and the rejection of ink in the non-image areas of a reverse lithographic resinous printing plate.

Another object of the invention is to decrease the sensitivity of application of background liquid in a reverse lithographic duplicating process.

A still further object of the present invention is the provision of a novel and unique method and means for inking and wetting a printing master with hydrophilic ink and an oleophilic background fountain solution.

These and many other objects and attendant advantages of the invention will become apparent as the description proceeds.

An improved painting system for reverse lithography is provided in accordance with the invention by applying an aqueous-miscible ink to the surface of a porous inking roller impregnated with an oily fountain solution. The mixture of ink and oil is applied from the inking roller to the printing master and the oil selectively deposits on the oleophilic background portions of the master while the water-miscible ink selectively deposits on the image areas.

The compressible and absorbent surface of the roller when contacted with the master is found to deform around the slightly raised, porous, roughened image characters and to selectively apply ink to the image characters and to maintain a thin film of oil on the smoother surrounding background areas. Excellent prints are produced on a continuous basis.

The single printing and oil application roller may contain an internal reservoir of oil which is automatically metered onto the printing master by controlling the relative pressure between the master and the roller and the amount of oil necessary has been found to be less critical than in previously practiced systemsln a further preferred feature in accordance with the invention, the top surface of the inking roller is grooved and the oil is selectively applied from the sides of the grooves while the ink is selectively applied from the top surface of the adjoining ridges. A pair of the grooved rollers with the ridges of the rollers off-set to overlap the grooves of the other roller may be utilized to assure total inking of the master.

The invention will now become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of rollers in a reverse lithographic printing system according to the invention;

FIG. 2 is a front elevation view partially in section of the combined inking and fountain roller of the invention;

FIG. 3 is a front elevational view of a grooved inkingfountain roller;

FIG. 4 is an enlarged schematic illustration of the application of ink and oil to the master from one raised ridge of a stationary grooved inking roller;

FIG. 5 is a schematic illustration of a printing system incorporating a pair of grooved inking-fountain rollers;

FIG. 6 is a view taken along the line 6-6 of FIG. 5;

FIG. 7 is a schematic illustration of a further embodiment of a printing system in accordance with the invention;

.FIG. 8 is an end view partly in section of the inking rollers of the system of FIG. 7;

FIG. 9 is a schematic view of a further embodiment of a printing system; and

FIG. 10 is a view taken along the line 10-10 of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2, the printing master 10 is secured to a plate cylinder 20. An aqueous miscible ink is applied from an ink fountain 12 to a fountain roller 14. A doctor blade 16 controls the amount of ink applied by fountain roller 14 to the porous inking roller 18. The inking roller 18 includes a porous, absorbent sleeve 22 saturated with an oleophilic background liquid. Suitably, the mandrel 24 for the roller 18 contains perforations 26 and forms a reservoir 28 for the oleophilic background liquid 30.

As the rollers rotate, the oleophilic liquid 30 saturates the sleeve 22 and the ink applied to the surface 32 of the inking roller 18 mixes with the oil and the mixture is applied to the surface of the printing master 10. The ink will be selectively absorbed by the image areas and the oleophilic liquid will be selectively applied to'the smooth background areas and the latter areas will reject the ink. The inked image pattern is transferred to a sheet 34 of paper or other material to be printed or decorated being fed between impression cylinder 36, and the master cylinder 20. Alternatively, the inked image can be transferred to a blanket cylinder, not shown, and printed on the paper by an off-set process.

The printing master 10 is suitably formed of a base sheet material which is preferentially wettable by a liquid immiscible with water or with water miscible liquids. The base sheet is preferably formed of synthetic organic resins such as polystyrene.

The surface of the smooth base sheet may be evenly coarsened or roughened as disclosed in copending application, Ser. No. 3,160, filed Jan. 15, 1970, now abandoned entitled Printing Master for Reverse Lithography, the disclosure of which is incorporated herein by reference. This treatment forms a matte, grained surface having increased ability to retain the ink repelling liquid within the channels, irregularities or pockets formed by the roughening treatment.

The image pattern or areas are suitably formed of an organic resin having good tolerance to aqueous miscible liquids such as glycols and having very poor tolerance to glycol repelling liquids such as hydrocarbon oils. Suitable resins are polystyrene or copolymer of vinylacetate and ethylene and polyester resins such as Vitel 222 (Goodyear Rubber Co.). The image areas may contain pigment particles such as carbon black or zinc oxide dispersed in the resin binder film which can provide a rough surface for holding ink within the interstitial spaces between the pigment particles.

The image areas are preferably formed from an electrophotoconductive pigment such as zinc oxide dispersed in an organic binder resin but may also be formed of other photoconductive materials such as selenium, cadmium sulfide or cadmium selenid'e. The printing master may be prepared according to the procedure disclosed in application, Ser. No. 30,753, filed Apr. 22, 1970, now US. Pat. No. 3,648,608, for Method and Means for Making a Duplicating Master, the disclosure of which is incorporated herein by reference.

An ink composition suitable for use in the reverse lithographic process of the invention comprises an aqueous or polyhydric alcohol thinner, a film forming binder resin dispersed in the thinner and suitable dyes or pigments as coloring agents. Ink compositions for practicing the process of the invention are disclosed in co-pending applications, Ser. No. 3,096, filed Jan. 15, 1970, entitled, Ink for Reverse Lithography, and Ser. No. 533, filed Jan. 5, 1970, entitled, Ink Composition for Reverse Lithography, the disclosure of which are incorporated herein by reference.

The oleophilic background liquid is generally a hydrocarbon oil, a silicone oil or other hydrophilic ink repelling liquid having preferential adsorptivity for the smooth background areas of the printing master. Superior performance is obtained with high boiling aliphatic hydrocarbons such as kerosene oil fractions distilling between 520 to 560 F and other product, Deodorized 400 oil, distills between about 390 to 450 F. lsopar G is a mineral oil fraction distilling between about310 to 350 F. More copies per plate and better performance are obtained when the non-polar liquid is also a nonsolvent for the material forming the base sheet of the printing master. For this reason, when polystyrene is utilized in the printing master, liquids having a high percentage of aromatic hydrocarbons are preferably avoided to alleviate swelling and dissolution of the printing master.

In accordance with another aspect of the invention, it has surprisingly been discovered that better print quality and less criticality in the rate of metering the oleophilic liquid to the printing master are achieved when the ink is premixed with up to 15 percent by weight, suitably about 10-12 percent by weight of the oleophilic repelling liquid, such as Deodorized 400 oil. The hydrophilic ink and the oil are premixed and the mixture is added to the ink fountain 12. The ink will be blended with additional amounts of oil as'it passes over the porous inking roller 18 and the oil and ink will be redistributed between background and image when they contact the printing master l0.

The porous, absorbent outer sleeve 18 contains an interconnected network of open cellular pores. The matrix is formed of a tough, abrasion resistant, resilient synthetic elastomer having good wetting properties for the oleophilic fountain solution. The sleeve should be dimensionally stable and should dispense fountain solution on light pressure contact with the printing master. The void percentage can vary over wide limits. At a void volume of percent sufficient matrix elastomer remains to provide the desired compression and resiliency properties. The void volume should be atleast 20 percent to provide sufficient retention of liquid for quickly dispensing a controlled amount of liquid at working pressure. Pore size should be uniform and fairly small, typically below 100 microns suitable about -20 microns. Tensile and tear strength must be high. Hardness as measured by Shore A durometer can range from about -35, preferably about -30.

The porous elastomer sleeve can be fabricated from many different polymer systems such as natural or synthetic diene latices, polyolefms such as polyethylene, polypropylene or polyvinyl chloride, polyamides such as Nylon or polyurethanes. The open pore structure can be provided by the controlled sintering of particles of the resin or by the use of chemical or glass blowing agents.

A suitable material known as Micro-well (Elastolabs Corp.) is an abrasion-resistant, polyurethane material having a 70 percent void density containing an interconnected network of 13-14 micron open pores, and having a Shore A hardness of about 27 and a specific gravity of 1.30 to 1.35. Light finger pressure readily dispenses the oleophilic liquid at the depressed location in controlled amounts without excessive flooding of the surface. The small diameter pores act as capillaries to pump the liquid from the internal part of the sleeve to near the surface. The near surface capillaries act as a dispensing valve to controllably meter the liquid onto the surface of the printing master.

The sleeve can be initially charged with oleophilic fountain solution and can supply the solution to the master for a finite amount of copies before recharging is necessary on a batch or continuous basis. A preferred manner of recharging the sleeve is to continuously sup ply fountain solution to the sleeve from a reservoir. As illustrated in FIG. 2, the reservoir 2% can be located in the interior of the mandrel 2d for roller 18. The hollow mandrel is closed by end plates 40, 42 and contains a series of perforations 26 communicating the reservoir 28 of liquid 30 with the interior portion of thesleeve. The liquid movesoutwardly through the interconnecting capillaries to near the surface 32 of the roll. The reservoir 28 can be refilled through plug 50 in end plate 42. It was further discovered that when the printing system was operated with plug 50 removed, more liquid was dispensed.

The outer surface pores of the sleeve exhibits some tendency to close on application of pressure from the print master. Referring now to FIG. 3, this problem is obviated by forming a plurality of spaced, parallel, vertical grooves 60 in the face of the sleeve, such that the grooves 60 alternate with ridges 62. Thus, when the grooved sleeve 64 contacts the printing master it), the oil will be dispensed from the side walls 66 of the ridges 62. The ink is only received on the top surface 68 of the ridges 64 and the ridges 64 selectively transfer the ink to the image areas of the master.

Since incomplete inking of the master may occur, it is preferred to utilize a set of grooved inking rollers 70, 72 as illustrated in FIGS. 5 and 6. The inking rollers are in contact with a roller 73. The fountain roller T4 is transported back and forth between the ink fountain l2 and the roller 75 of the inking train in order to control the amount of ink applied to the porous inking rollers 70, 72. The grooves 76 are slightly narrower than the ridges 78 and one of the rolls is off-set the width of a groove 76 such that the opposing ridges 78 from each roll overlap the opposite grooves 76 of the other roll. Thus, complete inking of the plate 10 is assured and high quality prints are obtained on sheet 34 passing between the master cylinder 20and impression roller 36. In an illustrative embodiment, the sleeve has a 2 inch outer diameter and a 1 inch inner diameter. The grooves are Vi inch deep and inch long while the ridges have a top face length of V2 inch. A fresh printing master should be conditioned before use by rubbing the sleeve against the plate to apply an initial film of oil on the background areas, and deposit some ink in the image areas. The plate will then be ready to deliver high quality prints on start-up of the printing press.

in the preferred printing process using the porous roller, according to the invention, there are two distinct phases: preoiling and printing. During the preoiling stage, the porous rollers 18 are held stationary, while the master cylinder 20 carrying the printing master 10 is rotated with the master in contact with the rollers. Referring now to FIG. 4, the imprint of one of the high portions or ridges 68 of the porous inking roller on the master it) is shown. The ink on the surface of the porous roller tends to seal the pores therein. This is especially true since, with a pigmented ink, the pigment particles tend to clog the pores of the porous roller. The oil, however, escapes from the side walls of the groove which side walls are compressed by the contact with the master. Thus, as shown in FIG. '4, the oil 80 tends to surround the portion of the roller in contact with the printing master. Therefore, as the master cylinder 20 rotates, causing the master to rub against the stationary porous rollers, the portion of the oil 82 squeezed out in front of the roller 70, 72, wets the background area 84 of the master and coats it. In the image area 86 most of the oil deposited thereon is immediately squeezed off by the porous roller immediately therebehind, and what little bit is left is absorbed into the porous character 86. The porous roller in contact. with the image also coats theimage with ink preventing any further deposition of oil. In this way, at the end of the preoiling, the background areas 84 of the master are coated with oil, while the image areas 86 are relatively free of oil and have some ink coated thereon.

The second phase of the operation of the system is the printing phase. During printing, the porous rollers 70, 72 rotate in synchronism with the master cylinder 20 so that there is rolling contact between them rather than the sliding contact which occurred during the preoiling phase. The ink deposited on the surface of the porous rollers then inks the image portions 86 of the master while the oil from the interior of the porous roller replenishes the supply of oil on the background 84. The amount of force exerted by the master on the porous inking roller is fairly substantial and may be on the order of about 50 pounds. Rather strong pressure is needed in order to squeeze out a sufficient amount of oil from the side walls of the grooves of the porous rollers.

A further and most preferred embodiment of a printing system is illustrated in FIGS. 7 and 8. This system incorporates means to regulate the rate of ink and oil delivery to the printing master. Even though the ink is much more viscous than the oil, it has been found that the ink tends to spray from the fountain roller and other rollers in the inking train. Referring now to FIG. 7, a much improved ink delivery train is provided by means of an ink delivery roller 90 in contact with both of the grooved inking rollers 70, 72:.

The inking roller 90 includes a central hollow, perforated mandrel 92 covered with a sleeve 9d of a soft, re-

silient compressible cellular material such as an open cell foamed organic resin such as polystyrene or polyurethane. The pores of the sleeve are fairly large to permit dispensing the pigmented, viscous ink. The resin may be modified to increase its hydrophilic properties to insure good wick action to dispense the ink from the ink reservoir 96 within the hollow mandrel 92.

The outer surface of the porous sleeve 94 may optionally be covered with a tubular band 98 of an open mesh fabric such as Nylon. This band 98 serves to retain the sleeve 94 on the mandrel and to decrease the abrasion of the sleeve 94 during rolling contact with the inking rollers 70, 72. The ink delivery roller assembly 90 may be provided as a disposable, batch cartridge which is thrown away after the ink supply is exhausted. The ink contained in the reservoir within the hollow mandrel may be a glycol based carbon black, acid dye, shellac binder ink as disclosed in application Ser. No. 533 and need not be premixed with oil.

As the rotating ink delivery roller 90 contacts each inking roller 70, 72 the sleeve 94 is compressed and ink is dispensed onto theportion of the top surface 68 of the ridges 62 of the sleeve 64 in contact with the sleeve 94. As the roller 90 passes out of contact with the inking roller 70, 72, the sleeve expands to its original shape and absorbs the excess ink back into the sleeve 94. The sleeve 94 is much softer than the sleeve 64 of the inking roller and is therefore preferentially compressed when in pressure contact with the roller 70, 72. Therefore, little oil is dispensed from the inking roller 70, 72 during inking. The oil is dispensed from the side walls 66 of the ridges when the inking rollers 70, 72 contact the printing master 10.

Referring now to FIG. 8, the oil delivery from inking rollers 70, 72 is regulated by installing a rotating seal 100 atone end of each of the rollers 70, 72. The seal includes an O-ring 102 installed between the hollow stub shaft 104 of each roller and the housing 106. A line 108 containing a valve 110 is connected to the housing 106 and to a closed cannister 112 which, however, is open to ambient pressure. During rotation of the rollers 70, 72 a slight vacuum is formed as the oil is dispensed through the hollow mandrel 24 into the porous sleeve 22. The seal 100 maintains the decreased pressure and prevents equalization of pressure with the ambient at the rotating seal. The pressure within the reservoir 28 is equalized with the closed cannister 112 by means of the valve 110 which opens in the presence of the vacuum, and thus serves to regulate the rate of oil delivery through the slotted porous sleeve.

A further embodiment of a printing system is illustrated in FIGS. 9 and 10. Oil and ink are applied to the master 202 on the master cylinder 200 by means of an oil charged porous roller 204. The roller 204 is formed of a perforated mandrel 206 forming a reservoir for the oil supply. A porous, absorbent, sleeve 208 which may be formed of the materials previously described is mounted on the mandrel 206. In order to assure an adequate oil supply at the surface of the sleeve 208, a series of spaced vertical slits 210 are cut into the roller, for example, the sleeve can be about V1 inch thick and the slits are Va inch apart and about inch deep.

The ink reservoir for the system is contained within a screen roller 212. The roller 212 includes an axial rotatable rod 214 supporting end plates 216. A cylindrical screen 218, suitably a 100 mesh metal screen is mounted on the end plates 216.

The ink is transferred from the surface of screen 218 to the roller 204 by means of a soft, porous transfer r01 ler 220 which rotates in pressure contact with the screen roller 212 and the oil charged roller 204. The roller 220 includes a central core 222 supporting a soft sleeve 224 of compressible foam. The transfer roller 220 rotating in pressure contact with the roller 204 causes the ink and oil to mix within the pores of the foam sleeve 224 and aids in insuring the application of a smooth, uniform layer of ink and oil to the surface of the oil-charged roller 204 and to regulate the thickness of the ink coating. The sleeve 224 of the porous transfer roller 220 can be made of any plastic foam which is not attacked by the ink or oil and is preferably more resilient than the sleeve 208 of the oil loaded roller 204.

The printing system of the invention provides a much simplified apparatus for printing by reverse lithography and eliminates many rollers previously thought necessary while not being as sensitive to replenishing background fountain solution.

It is to be understood that only preferred embodiments of the invention have been described and that numerous substitutions, modifications and alterations, are all permissible without departing from the spirit and scope of the invention as described in the following claims.

What is claimed is:

1. A system for inking a printing master having shaped image regions which preferentially absorb water-miscible inks and background regions which do not absorb water-miscible inks, comprising:

roller means including a rigid mandrel having an outer sleeve of a porous, liquid absorbent, compressible material;

said sleeve outer surface containing a plurality of grooves alternating with ridges, said ridges and grooves being disposed transverse to the axis of said mandrel;

means for applying water-miscible ink directly to the surface of said outer sleeve;

means for applying hydrophobic liquid to said surface of said outer sleeve from the interior of said roller means; and

means for rolling said roller means to roll the surface of said sleeve over the surface of said master, whereby said ink is selectively deposited on said image regions and said liquid coats said background regions.

2. A system according to claim 1 in which said sleeve is formed of a tough, abrasion-resistant, resilient synthetic elastomer containing an interconnected network of open cellular pores.

3. A system according'to claim 2 in which said elastomer is a polyurethane having a void volume between 20 and percent.

4. A system according to claim 1 in which said mandrel is hollow forming a reservoir for said hydrophobic liquid and said mandrel is perforated for applying said liquid to the surrounding porous, absorbent sleeve.

5. A system according to claim 4 further including hydrophobic liquid regulating means connected between said mandrel and said reservoir, said hydrophobic liquid regulating means including valve means operable responsive to a pressure drop caused by loss of liquid from said mandrel for enabling replenishment of said liquid from said reservoir.

6. A system according to claim in which said regulating means includes a rotary seal connected to an end member of said mandrel, a housing surrounding said seal, a closed member and conduit means connecting said housing to said closed member.

7. A system according to claim 4 in which said ink applying means includes an ink delivery roller having a soft, porous, ink loaded outer sleeve in contact with the absorbent sleeve of said roller means.

8. A system according to claim 7 in which said ink delivery roller includes a hollow, perforated mandrel forming a reservoir for said ink and said soft, porous sleeve is received on said mandrel.

9. A system according to claim 7 in which said ink applying means includes a hollow roller having a perforated outer cover enclosing a reservoir for said ink and said soft porous sleeve is in pressure contact with said cover and the outer sleeve of said roller means.

10. A system according to claim 1 in which said means for applying ink includes a fountain roller for applying ink to the outer surfaces of said ridges.

1 l. A system according to claim 1 in which said roller means includes a plurality of rollers having said grooved sleeves for contacting said master; the ridges of a sleeve of at least one roller overlapping the path of travel of the grooves of another sleeve over said master. 12. A system for inking a printing master having shaped image regions which preferentially absorb water-miscible inks and background regions which do not absorb water-miscible inks, comprising:

roller means including a rigid mandrel containing an outer sleeve of porous, liquid absorbent, compressible material; said sleeve outer surface containing a plurality of spaced slits, means for applying water-miscible ink directly to the surface of said outer sleeve; means for applying hydrophobic liquid to said surface of said outer sleeve from the interior of said roller means; and means for rolling said roller means to roll the surface of said sleeve over the surface of said master, whereby said ink is selectively deposited on said image regions and said liquid coats said background regions. 13. A system according to claim 12 in which said slits are disposed perpendicular to the axis of said mandrel. 

2. A system according to claim 1 in which said sleeve is formed of a tough, abrasion-resistant, resilient synthetic elastomer containing an interconnected network of open cellular pores.
 3. A system according to claim 2 in which said elastomer is a polyurethane having a void volume between 20 and 80 percent.
 4. A system according to claim 1 in which said mandrel is hollow forming a reservoir for said hydrophobic liquid and said mandrel is perforated for applying said liquid to the surrounding porous, absorbent sleeve.
 5. A system according to claim 4 further including hydrophobic liquid regulating means connected between said mandrel and said reservoir, said hydrophobic liquid regulating means including valve means operable responsive to a pressure drop caused by loss of liquid from said mandrel for enabling replenishment of said liquid from said reservoir.
 6. A system according to claim 5 in which said regulating means includes a rotary seal connected to an end member of said mandrel, a housing surrounding said seal, a closed member and conduit means connecting said housing to said closed member.
 7. A system according to claim 4 in which said ink applying means includes an ink delivery roller having a soft, porous, ink loaded outer sleeve in contact with the absorbent sleeve of said roller means.
 8. A system according to claim 7 in which said ink delivery roller includes a hollow, perforated mandrel forming a reservoir for said ink and said soft, porous sleeve is received on said mandrel.
 9. A system according to claim 7 in which said ink applying means includes a hollow roller having a perforated outer cover enclosing a reservoir for said ink and said soft porous sleeve is in pressure contact with said cover and the outer sleeve of said roller means.
 10. A system according to claim 1 in which said means for applying ink includes a fountain roller for applying ink to the outer surfaces of said ridges.
 11. A system according to claim 1 in which said roller means includes a plurality of rollers having said grooved sleeves for contacting said master; the ridges of a sleeve of at least one roller overlapping the path of travel of the grooves of another sleeve over said master.
 12. A system for inking a printing master having shaped image regions which preferentially absorb water-miscible inks and background regions which do not absorb water-miscible inks, comprising: roller means including a rigid mandrel containing an outer sleeve of porous, liquid absorbent, compressible material; said sleeve outer surface containing a plurality of spaced slits, means for applying water-miscible ink directly to the surface of said outer sleeve; means for applying hydrophobic liquid to said surface of said outer sleeve from the interior of said roller means; and means for rolling said roller means to roll the surface of said sleeve over the surface of said master, whereby said ink is selectively deposited on said image regions and said liquid coats said background regions.
 13. A system according to claim 12 in which said slits are disposed perpendicular to the axis of said mandrel. 